FIG. 1 is a schematic perspective view showing an overall configuration of a general active matrix type display device.
As shown in FIG. 1, this display device has a flat structure comprising a display panel 10 and provided with a pair of glass substrates 11 and 12 and an electrooptic material held between them. As the electrooptic material, use is made of for example a liquid crystal 13.
The glass substrate 11 is formed with a display unit 14 and a peripheral drive unit integratedly formed. The drive unit formed on the glass substrate 11 includes a vertical drive circuit 15 and a horizontal drive circuit 16. One peripheral edge of the substrate 11 is formed with terminals 17 for external connection. The terminals 17 are connected via interconnects 18 to the vertical drive circuit 15 and the horizontal drive circuit 16.
The display unit 14 is formed with pixel circuits, each including a pixel electrode 14a and a thin film transistor (TFT) 14b driving the same, in a matrix. A gate interconnect 19G is formed for every row and a signal interconnect 19S is formed for every column of the matrix array of the pixel circuits. Each pixel circuit is arranged at an intersecting portion of two interconnects, a gate electrode of the TFT 14b is connected to a corresponding gate interconnect 19G, a drain region is connected to a corresponding pixel electrode 14a, and a source region is connected to the corresponding signal interconnect 19S. The gate interconnects 19G are connected to the vertical drive circuit 15, and the signal interconnects 19S are connected to the horizontal drive circuit 16.
On the other hand, an inner surface of the glass substrate 12 facing the glass substrate 11 is formed with not shown a counter electrode. The counter electrode is arranged facing the pixel electrodes 14a. Individual pixels are formed by the pixel electrodes 14a, the counter electrode, and the liquid crystal 13 held between the two.
A TFT 14b, as explained above, is provided corresponding to each pixel and switches each pixel ON and OFF. In the present specification, a TFT for pixel switching formed in the display unit 14 will be sometimes referred to as a “pixel transistor”. On the other hand, the peripheral vertical drive circuit 15 and the horizontal drive circuit 16 also include TFTs (thin film transistors) formed by integration simultaneously parallel to the pixel transistors. Below, in this specification, the TFTs configuring the peripheral drive circuits 15 and 16 will be sometimes referred to as “peripheral transistors”. Both the pixel transistors and the peripheral transistors comprise TFTs (thin film transistors) formed by stacking a polycrystalline semiconductor thin film (for example, polycrystalline silicon film) and gate electrodes via gate insulating films.
FIG. 2 is a view of an example of the configuration of a projection type display (hereinafter, referred to as a “projector”) using the liquid crystal display panel 10 shown in FIG. 1.
This projector 20 has, as shown in FIG. 2, a structure comprised of a light source 21, a transmission type liquid crystal display panel 10A sandwiched by a pair of polarization plates 22 and 23, and an enlargement projection optical system 24 arranged in order along the optical axis. Here, the liquid crystal display panel 10A has the flat structure shown in FIG. 1. The light source 21 is configured by an elliptical reflection mirror 25 and a lamp 26 arranged at the center thereof and radiates high intensity illumination light to an arrangement direction of the liquid crystal display panel 10A (front side). The front surface of the light source 21 is provided with a filter 27 which absorbs the unnecessary UV-ray component and infrared ray component included in the illumination light. Further in front of this is arranged a condenser lens 28 which condenses the illumination light and makes it strike the entire surface of the light incident side of the liquid crystal display panel 10A. The enlargement projection optical system 24 is arranged on the light transmission side (front) of the liquid crystal display panel 10A and enlarges and projects an image formed by a display unit 14A of the liquid crystal display panel 10A to the front. The enlarged and projected image is formed on a screen 29.
The liquid crystal display panel 10A is divided into for example a normally white mode display unit 14A and a peripheral nondisplay unit 212. The nondisplay unit 14B includes for example a peripheral drive circuit. A pair of polarization plates 22 and 23 are arranged so that their polarization axes are orthogonal. The display unit 14A of the liquid crystal display panel 10A includes a twist oriented liquid crystal and has an optical rotatory power of 90 degrees with respect to the incident light. On the other hand, the pair of polarization plates 22 and 23 are crossed-Nicol arranged. Accordingly, linearly polarized light passing through the incident side polarization plate 22 is rotated about its polarization axis 90 degrees by the liquid crystal included in the display unit 14A and passes through the emission side polarization plate 23. Accordingly, a normally white mode display is obtained, and an enlarged and projected image is formed on the screen 29.
Projection display devices (projectors) using liquid crystal display device (LCD) in this way are rapidly spreading along with the improvement of brightness since large screen displays are easily obtained.
A projector is a device having a strong light source, controlling the image by a liquid crystal display acting as a light valve, and enlarging and projecting the image information. Strong light strikes the liquid crystal display device. Due to requests for further improvement of the screen luminance or reduction of size of projectors, the amount of incident light per unit area of the liquid crystal display device is becoming increasingly larger.
On the other hand, reflection light etc. generated inside the optical system or liquid crystal display device due to strong incident light strikes the active layers of some pixel transistors, so leakage current (hereinafter referred to as a “photo-leakage current”) caused by optical excitation is caused. An increase of the photo-leakage current becomes a cause of flicker and roughness of the screen, so gives a fatal defect to the image quality.
In the past, in order to cope with the increase of the amount of incident light, a light shielding structure for shielding the pixel transistors from the top and the bottom has been formed. By arranging metallic films or silicide films in a manner covering the incident side and the emission side of the pixel transistors and optimizing the shapes and dimensions thereof, it was possible to shield the pixel transistors from light and hold or improve the image quality.
However, the light shielding structure inevitably sacrifices the numerical aperture of the pixels, so runs contrary to the requests for higher luminance of the screen. Due to the necessity of improvement of the numerical aperture of the liquid crystal display panel, it has already become difficult to sufficiently secure the light shielding area.